System for protecting petroleum tanks and tank farms against lightning and electrical sparks



Nov. 12, 1929. w. DODD 1,735,530

SYSTEM FOR PROTECTING PETROLEUM TANKS AND TANK FARMS AGAINST LIGHTNING AND ELECTRICAL SPARKS Filed May 31, 1927 m m U a w. d d WW M Patented Nov. 12, 1929 UNITED STATES WEST DODD, F DES MOINES, IOWA SYSTEM FOR PROTECTING PETROLEUM TANKS AND TANK FARMS AGAINST LIGHT- NING AND ELECTRICAL SPARKS Application filed May 31, 1927. Serial No. 195,398.

My present invention has for its general purpose to provide a system for protecting petroleum tanks and tank farms against lightv ning and electrical sparks. It is more particularly my purpose in this connection to provide such a system comprising apparatus including elements so constructed and arranged that sparking and direct hits at the tanks will be prevented.

A further purpose is to provide such an apparatus whereby electrical charges from the earth entering the conductive parts of the tanks will be expelled from the entlre tank structure and conducted away from the tanks to points of discharge located a safe distance from and preferably above the roofs of the tanks.

This application is a continuation in part of my application theretofore filed on May 15, 1926, Serial No. 109,310, and lssued as Patent No. 1,691,340, dated November 13,

lVith these and other objects in view, my invention consists in the construction, ar-

5 rangement and combination of the various parts of my system, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawings, in

Figure 1 shows a diagrammatic plan view of a tank farm including a series of tanks of the well-known sectional built-up metallic construction having installed in connection therewith apparatus embodying my system.

Figure 2 is an elevation partly in section illustrating part of the apparatus taken on the line 22 of Figure 1; and

Figure 3 is a top or plan view of one of the tanks equipped with my apparatus.

It is a fact of general knowledge that in oil fields and other places where petroleum is stored in tanks, immense losses occur as 5 result of fire caused by electrical sparks and lightning.

Petroleum tank fires from lightning causes may occur in two diiferent ways, viz by electro-static sparks among inflammable gases at the instant of a lightning discharge at some distance, or by a direct lightning hit at the tank.

Sheets of metal are usually nailed on a Wood roof of a tank. These metallic sheets are seldom in metallic union and sparks occur in the electrical resistance gaps between these metallic sheets, if a lightning discharge is near, or through its influence if near a connecting pipe line, and these sparks in inflammable gases will start a fire, just as in the inflammable gases in an automobile engine.

The other and surer Way is by a direct lightning hit at the tank rim where the inflammable gases most generously escape.

I may here state :Lightning or electrostatic sparks or so-called lightning strokes result from previous electric conditions induced or attracted from earth into the metallie or conductive parts of the tank by an approaching overhead oppositely electrically charged cloud.

When a cloud, carrying an electrical charge, is passing, it induces a complementary charge, of opposite sign, on a substantially corresponding area of the earths surface, and the metallic pipe lines, associated with the tanks and extending out into the earth electrical field or charge, readily focus the earth charge on the tanks.

When a cloud discharges by a lightning flash, the tanks instantly discharge to earth at the same instant and that endangers the tank, either by electro-static sparks on the roof in any gaps between the metallic parts, or by a direct lightning hit.

When a tank fire occurs by a direct lightning hit, the flash is uniformly at the tank rim or winch near the tank rim. This is because of the rather flat tank roof, by which the law of repellence of similar sign electricity can readily focalize the induced electrical charge seeking its path of least resistance through the wall of the tank more densely at the tank rim and among the inflammable escaping gases, than anywhere else on the tank.

In providing the apparatus comprising my -system, I have in view the following additional principles:

First. I desire to so far as possible prevent the accumulation of electrical charges on the tank. I do this in the belief that where there is less electrical charge, there is less likelihood of a spark or direct hit.

Second. I desire to provide means for preventing either a'spark or direct hit on or at the tank.

These desirable results are attained in the following manner:

In the drawings herewith, "Ihaveused the reference numerals 10 and 10 to indicate diagrammatically the roof and side wallofpetroleum tanks of the well known sectional metallic construction, which may be arranged in a farm as shown in Figure 1.

14 :is a protecting wall surrounding the tank.

19 and 20 designate the electrically conducti-ve joints "between the sections of the tank roof.

Ordinarily,there are pipe lines 12 leading to'and fromthe farm and branches 19/ connecting'the main pipe lines with the respectivetanks.

In order, sofar as may be possible'to avoid a strongelectricalcharge in thebodies of the tanks from the earth electrical charge through theipipe lines, 'Ierect tallmetallic towers 16 with terminalpoints 18 on the pipelines at safe distances outside of the tank farm. These towers and their :points serve two important functions, one ofwhich is to offer a preferred :path for *the lightning discharge,

rather than among 1 the =tanks, and the other .to silently discharge electricity as much as may be in order to minimize 'the lightning "stroke-and even tend to preventeit.

As stated thelaw of self-repulsionof similar sign electricityfocuses any charge ofelectricity, induced on a tank more densely at the tank rim than: anywhere else on the-tank roof. For 'that reason,a lightningrhit or-discharge isvalways at t-herim of any ordinary tank.

In order to provide'a'gainst-such lightning discharge at the tank run and also lessen 'the sparkingpossibilities'onztheitank roof, I

arrange. aroundand apart from each tank the .posts 22, the terminal .points of which are preferably-some higherthan the tanks, but not as high as the towerpoints 18. The posts 22' are to be firmly set'inthe ground, prefer- :ably in concrete, and electrically connected by conductors. 24: with the tanlnatitheir bases adjacent to'the bottom of the:ta nk above-the surfaceof-the ground as-shown ln the drawing'rfor clearness, or, if desired, below the surface of the ground to thereby cover and conceal'the connectlons from exposure.

It 1s of XHLlCll'lHlPOItiLHCQ that these electric connections be'made at" the bottom oftlietank nections, even tolmelting,iand.any jointconnections made at the top of the tank would be subject to serious strains, due to the coefficient of tank expansion and contraction, creatin a push and pull strain tending to loosen the joints, which would be further augmented by wind pressure on the posts 22.

. The series .ofposts QQaround eachtank are preferably electrically connected together near their upper ends by metallic conductors such as the cable 26.

The effect of this arrangement of posts with their terminal points and tank connections pe rmits'the law of self-repulsions of similar sign electricity to focus or localize the electric discharge expelled from the tank at the points and connecting cable spaced from and surrounding the tanks and not at the tankrim as indicated by theline 28, Fig. 2. It is practicallythe same as'to set the-rim of the tank out and away from the places where gases escape, sothatlightning can only occur at'the surrounding points and cable, and never at'the tank.

To recapitulate and epitomize:

An electrically charged cloudinduces or attracts an electrical charge of opposite sign on the earths surface and about a tank.

The law of self-repulsion of similar sign electricity focusses and discharges the earths charge from the tank at-the-tank rimfrom.

which cause lightning occurs at the-tank rim.

This law of self repulsion of similar sign electricity is thekey to tank protection'when intelligent means for its operation is installed.

The means herein described are so related to the tank that this law is operative efiec- -tively and focusesand discharges the electricity expelled fromthe tanks to distantly localized pointsaway from the tanks on the surrounding equipment as described, and experimental research shows-the law is never failing, and a discharge of-electricity at any 1 place on-thetank impossible.

It will be understood that the parts ofthe system may beconstructed and-arranged in different Ways WltllOllh departing from the real spirit and purpose ofmy inventi0n, and itis-my intention to cover by my claimsany modified forms of structure or use of mechanical equivalents, which may bereasonably in cluded within their scope.

I claim as my invention:

1. In a systemfor protectingtanks against lightning, the combination with a tank'hav- .ing a roof and'side walls of electrically connected conductive material, of a plurality of metallic points spaced from the sidewallof 'the'tank and extending to a height greater than that of the tank, and means for electrically connecting the said points to the lower edge of the tank only, adjacent to the ground ing a roof and a Wall of conductive material electrically connected, of a plurality of metallic points spaced from the tank therearound, and extending to a greater height than that of the tank, means for electrically connecting each point to the bottom only of the tank at the ground or other support for the tank, and means for connecting the upper parts of the points together in series.

3. In a system for protecting tanks against lightning, the combination With a tank having a roof and side Walls of electrically connected conductive material, of a plurality of metallic posts having terminal points spaced from the side Wall of the tank, and means for electrically connecting the said posts to the lower edge of the tank only adjacent to the ground or other support for the tank. Des Moines, Iowa, April 27, 1927.

WEST DODD. 

